1. Field of the Invention
The present invention relates to a display screen management unit which switches and displays a plurality of screens. More particularly, the present invention relates to a display screen management unit which can reduce a screen resource required to switch screens and simultaneously display a screen before transition and a screen after transition.
2. Description of the Related Art
The term “screen” refers to information itself which is displayed on a display, but not to a display part (display), such as an LCD, liquid crystal, or the like. In other words, the screen is a unit which indicates a set of window instances which interact with a user. The term “screen resource” refers to a resource required to display a specific screen on a display. The screen resource is generated by a screen generating process and is discarded by a screen discarding process.
There is, for example, a conventional display screen management unit for switching and displaying a plurality of screens, that generates screen resources for all possible screens which can be displayed by a system when the system is started up. Such a display screen management unit switches and displays a plurality of screens in sequence by selecting screen resources to be switched from all screen resources which are generated when the system is started up.
However, since such a display screen management unit generates all screen resources when the system is started up, there are problems, such as a long time required to start up the system, a large size of memory required to store the generated screen resources, and the like. Therefore, the conventional display screen management unit needs to have a memory (e.g., a RAM or a flash memory) which can store the generated screen resources, or needs to store screen resources which cannot be stored in a memory into an external storage device, such as a hard disk or the like. If a screen resource is stored in a hard disk, swapping occurs with high frequency between the memory and the hard disk when screens are switched, so that screen switching is disadvantageously slowed, or the like.
In order to solve such a problem, Japanese Patent Laid-Open Publication No. 9-97158 discloses a display screen management unit which reduces a screen resource required to switch screens to effectively use a memory area. The conventional display screen management unit uses a screen flow diagram (see FIG. 19) in which currently displayed screens are associated with all possible screens which can become transition destinations (hereinafter referred to as all transition screens), to previously generate screen resources of all transition screens. When a screen is transitioned, a screen resource which is actually transitioned is selected from screen resources for all transition screens and is displayed, and screen resources which are not selected are discarded. Thereby, the conventional display screen management unit reduces a screen resource required to switch screens to effectively use a memory area, and prevents occurrence of swapping or the like to shorten a response time when switching screens.